Gem grinder having a pivotable rack and gear assembly

ABSTRACT

A pivotable rack and gear assembly for selectively locating and holding a geared frame at a chosen longitudinal position along a fixed axis while allowing the frame to be freely pivoted about the fixed axis. A geared frame is held on an elongated support shaft or post for movement along the shaft axis. It engages a longitudinally stationary rack in the form of a toothed plate which is free to &#39;&#39;&#39;&#39;float&#39;&#39;&#39;&#39; or pivot about the shaft axis within the confines of the frame. The rack is loosely held against the periphery of the shaft within a complementary recess through the frame and is free to pivot with the frame about the axis of the shaft. The rack is prevented from moving longitudinally and therefore provides a reaction member for movement of the frame along the post in response to rotation of the gear. The meshing gear is preferably driven by a worm drive assembly mounted within the frame for fine adjustment and locking of the frame at a selected longitudinal position. The gear may be moveably supported to permit its disengagement from the rack, allowing the frame to be freely moved along the shaft. The gear may also be powered by a motor and gear drive unit. A specific application of the apparatus is directed to support a dop arm assembly in a gem faceting machine.

United States Patent [191 Hoffman 1 June 11, 1974 GEM GRINDER HAVING A PlVOTABLE RACK AND GEAR ASSEMBLY Primary Examiner-Harold D. Whitehead Attorney, Agent, or Firm--Wells, St. John & Roberts [57] ABSTRACT A pivotable rack and gear assembly for selectively locating and holding a geared frame at a chosen longitudinal position along a fixed axis while allowing the frame to be freely pivoted about the fixed axis. A geared frame is held on an elongated support shaft or post for movement along the shaft axis. lt engages a longitudinally stationary rack, in the form of a toothed plate which is free to float or pivot about the shaft axis within the confines of the frame. The rack is loosely held against the periphery of the shaft within a complementary recess through the frame and is free to pivot with the frame about the axis of the shaft. The rack is prevented from moving longitudinally and therefore provides a reaction member for movement of the frame along the post in response to rotation of the gear. The meshing gear is preferably driven by a worm drive assembly mounted within the frame for fine adjustment and locking of the frame at a selected longitudinal position. The gear may be moveably supported to permit its disengagement from the rack, allowing the frame to be freely moved along the shaft. The gear may also be powered by a motor and gear drive unit. A specific application of the apparatus is directed to support a dop arm assembly in a gem faceting machine.

6 Claims, 12 Drawing; Figures PATENTEDJUN 1 1 1914 381528 9 SREEI 30? 3 m FIG1O 1 GEM GRINDER HAVING A PIVOTABLE RACK AND GEAR ASSEMBLY BACKGROUND OF THE INVENTION The present invention relates generally to the area of adjustable, pivotable rack and gear assemblies and specifically to apparatus for precisely positioning a tool or workpiece along an axis while allowing free pivotal movement of the tool or workpiece about the axis in a plane perpendicular to the axis.

One primary application of the present apparatus exists within the field of lapidary equipment utilized to cut or polish facets in precious or semi-precious stones. Such a machine is disclosed in my pending application Ser. No. 165,116 titled Faceting Machine and now abandoned. Such faceting machines generally include a powered lap or grinding wheel for rotation in a fixed horizontal plane. The gem is held by a dop elevationally adjacent the lap at theend of a dop arm which is angularly andelevationally positionable relative to the lap. The dop and dop arm are angularly positioned by a support yoke and are elevationally positionable by adjustment of a support frame mounted on a vertical support shaft or mast. Fine elevational adjustments are conventionally controlled by a separate adjusting screw assembly on the yoke. Horizontal pivotal movement of the dop is usually centered about the axis of this adjusting screw or another vertical shaft parallel to and apaft from the support shaft.

The primary disadvantage of the above apparatus is that the described adjustment requires pivotal movement of the dop assembly about more than one vertical shaft, presenting a possibility of compounding several errors within normal tolerance limits. Further, these types of assemblies require that the dop be supported a substantial distance from the supportshaft, creating more likelihood that-the support shaft will deflect or bend as leverage is applied at the end of the dop.

Other useful applications of the present invention may be readily envisioned in the support and positioning of many devices along a shaft, pole or mast. It permits free or controlled pivotal movement of the geared frame about the shaft axis while maintaining a selected longitudinal position by continuous contact with the floating rack.

Prior related U.S. Patents are: No. 2,579,666 to Hanes; No. 2,779,138 to Collar; No. 3,220,275 to Bruns; No. 2,119,710 to Holder, No. 2,620,698 to Warner; No. 2,688,881 to Crossland; No. 1,902,401 to Gunning; No. 2,924,077 to Le Tourneau; No. 2,933,298 to Dracalone; and No. 3,259,365 to Gibson,

1 Of the above cited U.S. Patents, none disclose a pivotable rack and pinion assembly similar to that comprising the present invention as disclosed in the following description and defined in the appended claims.

SUMMARY OF THE INVENTION The rack and gear assembly basically comprises a cylindrical member having an elongated rack loosely abutting its outer surface and restrained from longitudinal motion while free to slide about the outer surface of the cylindrical member. An encircling frame angularly locates the rack about the center axis of the cylindrical member. A gear assembly on the frame drivingly engages the rack for adjustment of the frame along the length of the cylindrical member.

It is a first object of this invention to provide a geared rack that allows pivotable movement of thesupported frame about the axis of the rack unit while eliminating relative motion between the rack and gear teeth.

Another object is to eliminate the usual need for two parallel pivot axes in a pivotable rack and gear assembly.

Another object is to provide practical elevational control of a dop arm in a gem faceting machine.

Other objects will be evident from the following detailed illustrative disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a gem faceting machine including the present invention;

FIG. 2 is a fragmentary pictorial view of the rack and gear assembly;

FIG. 3 is an enlarged cross-sectional view taken along line 33 in FIG. 1; I

FIG. 4 is an enlarged cross-sectional view taken along line 4-4 in FIG. 1;

FIG. 5 is a sectioned fragmentary elevation illustrating the apparatus in an operative condition;

FIG. 6 is an enlarged fragmentary front view taken along line 66 in FIG. 1;

FIG. 7 is an enlarged sectional plan view taken along line 7--7 in'FIG. l;

FIG. 8 is a fragmentary sectional view taken on line 8-8 in FIG. 7;

FIG. 9 is a sectional fragmentary plan view taken along line 9-9 in FIG 5;

FIG. 10 is a fragmentary elevational view of a second form of the invention utilizing a powered frame;

FIG. 11 is a fragmentary elevational viewof the apparatus utilizing a powered frame with a worm and worm wheel drive; and

FIG. 12 isa side view of the apparatus shown in FIG.

I DESCRIPTION OF A PREFERRED AND ALTERNATE EMBODIMENT Referring now to the drawings in more detail and especially to FIG. 1, a faceting machine similar to that disclosed in my pending application, Ser. No. 165,116,

is generally indicated by the reference numeral 10. Fa-

ceting machine 10 incorporates the pivotable rack and gear assembly of the present invention for precisely adjusting the height of a gem 12 from a lap 13 while allowing free pivotal movement of the gem in a horizontal plane. It should be noted that it is not the intent of this application to restrict use of the disclosed apparatus to such faceting machines. Other uses of the rack and gear assembly will occur to those designing equipthe present rack and gear assembly. Planar facets of pre-determined size and angular relationships are cut about gem 12 as it is held against the rotating lap 13. Theangular position of each gem facet is determined by adjustments provided on the dop arm assembly 11.

The depth of cut is controlled by positioning the dop arm assembly 11 along upright shaft or post 16 by engagement of a rack by a height adjusting assembly 18.

Base 14 rigidly supports the cylindrical post 16 in a vertical orientation. As shown in the drawings, post 16 is of substantial diameter to prevent bending along its center vertical axis as a result of forces applied to dop arm assembly 11.

An annular collar 17 of substantially larger outer diameter than post 16 is fixed to its upper end. A similar collar 19 is mounted to the lower end of post 16. Rack 20 is shown in the form of an elongated rectangular plate having outwardly protruding horizontal teeth. It is mounted between collars 17 and 19 directly adjacent the periphery of post 16 and longitudinally parallel to the post axis.

Friction pads 22 are fixed to each end of rack 20 for slidably engaging collars 17 and-19, allowing rack 20 to be freely rotated about the vertical axis of post 16. Pads 22 also prevent longitudinal movement of rack 20 along the post axis. Pads 22 are formed from material such as molybdenum disulfide-impregnated nylon or other wear-resistant, low friction material. Concentric grooves 23 are formed in the inwardly facing surfaces of collars 17 and 19 (FIGS. 7 and 8). They are utilized to reduce friction as rack 20 freely rotates about the axis of post '16.

Rack 20 is held in close proximity of the periphery of post 16 by the moveable frame member which includes height adjusting assembly 18 enclosed within a cast housing 24. Housing 24 includes an integral vertical guide sleeve section 25 having an elongated vertical bore to slidably receive post 16. A slot 26 extends the length of the bore to slidably receive rack 20 (FIGS. 2 and 9). Slot 26 is slightly larger in cross-section than rack 20, as shown in FIG. 9, allowing the frame 'to be moved along the longitudinal axis of post 16 without forcing rack 20 to move longitudinally therewith. However, as the frame is rotated horizontally about the axis of post 16, the rack is forced to rotate similarly as one side wall of slot 26 abuts a complementary side edge of rack 20.

It may be understood then, that although rack 20 is held stationary against vertical movement along the post axis, it pivots freely along with the frame about the post axis in a horizontal plane. This feature is notable in that a pinion gear 31 of height adjusting assembly 18 (described in more detail below) may remain stationary relative to rack 20 during rotation of the frame about the post axis. Wear between the meshing teeth of rack 20 and gear 31 iseliminated during rotation of the frame because they pivot in unison, whereas if the rack were immovable and continuous, about the post, the teeth of the pinion gear 31 would frictionally slide across the rack teeth. The resulting wear would eventually cause backlash, impairing precision positioning of the frame.

Pinion gear 31 is rigidly mounted for rotation on an elongated drive shaft 32 rotatably journalled in housing 24. The fixed rotational axisof pinion 31 and shaft 32 in housing 24 is perpendicular to and spaced from post 16 to facilitate mating engagement of pinion gear 31 with rack 20.

The separation between the axes is adjustable at the two journalled. portions of shaft 32 to aid in preventing backlash between rack 20 and pinion 31. One suchadjustment is made adjacent the end of shaft 32 that extends through a flanged bushing 34 (FIGS. 2 and 6). Bushing 34 is mounted in a slightly oversized hole in housing 24 for selectively adjusting pinion gear 31 toward or away from rack 20. Once adjusted, the bushing may be secured to housing 24 by a pair of cap screws 34 (FIG. 6) tightened against the bushing flange. A second, similar adjustment may be made with a circular cap plate 37 which provides a central second bushing 35 through which shaft 32 extends. Plate 37 is adjustably mounted to housing 24 by a spaced pair of screws '38 which extend through plate 37 to threadably engage the outward open end of housing 24. Screws 38 (FIG. 3) extend through holes in plate 37 that are slightly oversized to permit selective positioning of plate 37 and thereby adjust pinion gear 31 against rack 20.

To further aid in preventing backlash, rack 20 is longitudinally bowed slightly outward from the post 16-to urge the rack teeth against the teeth of gear 31.

Pinion gear 31 is driven to move the frame along rack 20 by a worm 50 and worm gear 46 which cooperatively mesh to form a worm drive assembly mounted within a retractable housing extending outwardly from plate 37 (FIGS. 1 and 6).

The outermost end of shaft 32 extends outwardly through housing 40 to threadably receive a nut 49.

Housing 40 is held stationary with respect to shaft 32 by nut 49 and a thrust bearing 47 on shaft 32 sandwiched between housing 40 and worm gear 46. Gear 46 is rigidly mounted to shaft 32 within housing 40 to operatively mesh with driving worm 50.

As may be seen in FIG. 4, worm 50 is affixed to a shaft which is journalled in housing 40 for rotation about an axis perpendicular to and spaced from the rotational axis of shaft 32. Shaft 51 is rotatably held within housing 40 by a first flanged bushing 53 adjacent one shaft end 48 and a second, similar bushing 56 at the opposite shaft end 54. Bushing'53 extends through a hole in housing 40 having a diameter slightly larger than the outside diameter of bushing 53 but smaller than the bushing flange. A screw 55 (FIGS. 4 and 6) extends through housing 40 to seat within an indentation in bushing 53. Screw 55 prevents bushing 53 from moving along the axis of shaft 51 but allows pivotal movement of the shaft in a vertical plane. Bushing 56 is also held within an oversized hole in housing 40 and is biased vertically downward in a radius about screw 55 by a spring 58 held within a vertical aperture in housing 40 by an adjusting screw 59. Shaft 51 and worm 50 are thereby urged downwardly against worm wheel 46 to prevent backlash between the engaged teeth. A cap 61 is removably affixed to housing 40 having a vertical elongated slot 62 designed to slidably receive the flanged end of bushing 56 and allow shaft end 54 to pass therethrough. Slot 62 is utilized to prevent longitudinal movement of bushing 56 along shaft 51 and to allow vertical movement of the bushing within the slot 62. Y

The frame may be selectively moved along post 16 by manually rotating a knob 52 affixed to shaft 51 at its end 48. Knob 52 rotates worm 50 which, in turn, operates whe'el 46 and pinion 31 to selectively move the frame up or down post 16.

A circular plate 57 is mounted to housing 40 inwardly from knob 52 with indicia placed thereon as a reference scale associated with a pointer on knob 52.

Each mark placed on plate 57 indicates the specific vertical distance from a fixed point or plane, such as lap 13, to the frame. I have found that for the purpose of gem faceting, the marks should each indicate a vertical frame movement of 0.002 inch.

Although not shown, other indicia may be utilized to indicate roughly the position of the frame on post 16. Marks vertically spaced along post 16, for example, when aligned with the top edge of guide 25 could indicate roughly the position of the frame.

The'gear ratios of the height adjusting assembly 18 may be varied with respect to theintended function of the present invention. When utilized as an adjustable support for a dop arm assembly as described above, I have found that a relatively low gear ratio, along with the anti-backlash features, facilitates highly accurate gem height positioning.

Because worm 50 and wheel 46 are non-reversible, the frame may be moved only by'rotation of knob 52an extremely slow processif a low gear ratio is used. Therefore, height adjusting assembly 18 is designed to be retractable along the axis of shaft 32 to disengage pinion 31 from the teeth along rack 20. The retracted position of assembly 18 is shown in FIG. 5. Once pinion 31 is. moved to the side of rack 20, the frame is free to slide easily and quickly to any position along post 16. During such sliding movement, the frame can also be rotatably moved about the center axis of post 16.

Assembly 18 is prevented from being completely detached from the frame by a collar stop 44 rigidly fixed to shaft 32. Stop 44 is positioned on shaft 32 between plate 37 and pinion 31 to abut plate 37 when pinion 31 is located at the side of rack 20.

An indexing finger 41 is provided on housing 40 to fit within a complementary opening 43 in plate 37. Finger 41 serves to prevent rotation of worm 50 about the axis of shaft 32 during operation of assembly 18.

The gear teeth of pinion 31 are slightly tapered toward the left side as seen in FIG. 5'to facilitate meshing re-engagement of pinion 31 with rack 20.

The operational sequence involved in precisely positioning the frame along post 16 involves two basically simple adjustments. First, the .operator may easily and quickly position the frame in the approximate desired position by retracting pinion 31 from rack 20 and sliding the frame to the desired position then re-engaging pinion 31 and rack 20. Care should be taken at this point to insure that finger 41 becomes firmly seated within opening 43 as illustrated in FIG. 2. The operator may then precisely position the frame along post 16 by turning knob 52 clockwise or counter-clockwise moving the frame up or down to a precise position indicated in plate 57. The frame may be pivoted freely about the post axis at any time. 1

FIGS. and 12 illustrate an alternate form of the invention in which the frame is powered by a conventional electric motor 64 to move up or down post 16.

The form illustrated by FIG. 10 utilizes motor 64 operatively connected to shaft 32 through intermediate, in line, reduction gearing of conventional form mounted in a housing 65.

FIGS. 11 and 12 illustrate a form similar to that pre- 6 viously described, only utilizing motor 64 in place of knob 52. A flanged housing 67 mounts motor 64 to housing 40 for direct attachment to worm 50.

Knob 52 of these forms is affixed directly to the outward end of the motor armature, and plate 57 is mounted to the motor to facilitate fine manual adjustments as described above. a

A reversible impulse switch (not illustrated) may be utilized to activate motor 64 to move the frame up or down post 16.

Use of motor 64 to power the frame up or down post 16 is particularly advantageous since gear 31 never need be disengaged from rack 20 for rough, quick positioning purposes. This advantage may quickly become evident to the operator of a faceting machine who disengages gear 31 from rack 20 and allows the dop assembly to fall downwardly onto the lap 13. The result could possibly be loosening of the gem on the dop and damage to the lap.

Further advantages of this form may readily be envisioned in other applications where, for example, motor 64 could be utilized in limited access areas of where the weight of the frame would prohibit manual adjustment efforts.

Various other changes and modifications may be made in the apparatus described above without departing from its intended spirit and scope. Therefore, only the following claims are intended to define my invention.

What I claim is:

1. In a gem faceting apparatus of the type including:

a base;

a powered horizontal .lap rotatably mounted on the base;

a dop arm located above the lap for support of a gem being polished or ground on the lap;

and a dop arm support assembly angularly locating the dop arm relative to the lap;

the improvement comprising:

a vertical post having an unobstructed continuous outer surface of constant circular cross-section centered along a vertical axis, said post being fixed to and extending upwardly from said base at a location alongside said lap;

a vertical elongated plate having a back surface abutting the post and an oppositely facing outer surface with a rack of parallel horizontal teeth projecting radially outward from the post axis;

means mounted on said post in operative engagement with said plate for preventing movement of the plate relative to the post in a direction parallel to the post axis while not restricting rotational movement of said plate about the post axis;

a rigid frame member mounting the dop arm support assembly to the post for elevationally locating the doparm relative to the lap, said frame member encircling said post for bearing engagement thereon and being apertured to receive said plate there through, said frame member having vertical surfaces abutting the plate for angularly locating said plate relative to said vertical axis; i I

and gear means on said frame for meshing engagement with the rack of teeth along said plate for permitting control of the vertical movement of the frame member relative to the post.

2. The improvement set out in claim 1 wherein said means mounted on the post in operative engagement withsaid plate comprises a pair of annular collars encircling and fixed to the post at opposite ends of the 7 v 8 plate, the collars being abutted by the'respective ends motor means mounted to said frame member having of the plate adjacent thereto. a driven shaft operatively connected to said first- 3. An assembly as set out in claim 1 wherein said gear named shaft for selectively rotating said firstmeans comprises a spur gear fixed to a shaft rotatably named shaft about said gear axis.

mounted to said frame member about a gear axis lying 6. An assembly as set out in claim 3 further comprisin a horizontal plane. ing:

4. An assembly as set out in claim 1 wherein said gear motor means mounted to said frame member having means comprises a spur gear fixed to a shaft rotatably a driven shaft operatively connected to said firstmounted to said frame member about a gear axis lying named shaft for selectively rotating said firstin a horizontal plane; 10 named shaft about said gear axis;

said shaft being moveable relative to said frame and manually engageable means on said driven shaft member along said gear axis a distance greater than for selectively permitting manual rotation of the the width of the teeth on said plate to thereby perdriven shaft and first-named shaft for adjustment of mit disengagement of the gear and teeth. the position of the frame member along the vertical 5. An assembly as set out in claim 3 further comprisaxis.

ing: 

1. In a gem faceting apparatus of the type including: a base; a powered horizontal lap rotatably mounted on the base; a dop arm located above the lap for support of a gem being polished or ground on the lap; and a dop arm support assembly angularly locating the dop arm relative to the lap; the improvement comprising: a vertical post having an unobstructed continuous outer surface of constant circular cross-section centered along a vertical axis, said post being fixed to and extending upwardly from said base at a location alongside said lap; a vertical elongated plate having a back surface abutting the post and an oppositely facing outer surface with a rack of parallel horizontal teeth projecting radially outward from the post axis; means mounted on said post in operative engagement with said plate for preventing movement of the plate relative to the post in a direction parallel to the post axis while not restricting rotational movement of said plate about the post axis; a rigid frame member mounting the dop arm support assembly to the post for elevationally locating the dop arm relative to the lap, said frame member encircling said post for bearing engagement thereon and being apertured to receive said plate therethrough, said frame member having vertical surfaces abutting the plate for angularly locating said plate relative to said vertical axis; and gear means on said frame for meshing engagement with the rack of teeth along said plate for permitting control of the vertical movement of the frame member relative to the post.
 2. The improvement set out in claim 1 wherein said means mounted on the post in operative engagement with said plate comprises a pair of annular collars encircling and fixed to the post at opposite ends of the plate, the collars being abutted by the respective ends of the plate adjacent thereto.
 3. An assembly as set out in claim 1 wherein said gear means comprises a spur gear fixed to a shaft rotatably mounted to said frame member about a gear axis lying in a horizontal plane.
 4. An assembly as set out in claim 1 wherein said gear means comprises a spur gear fixed to a shaft rotatably mounted to said frame member about a gear axis lying in a horizontal plane; said shaft being moveable relative to said frame member along said gear axis a distance greater than the width of the teeth on said plate to thereby permit disengagement of the gear and teeth.
 5. An assembly as set out in claim 3 further comprising: motor means mounted to said frame member having a driven shaft operatively connected to said first-named shaft for selectively rotating said first-named shaft about said gear axis.
 6. An assembly as set out in claim 3 further comprising: motor means mounted to said frame member having a driven shaft operatively connected to said first-named shaft for selectively rotating said first-named shaft about said gear axis; and manually engageable means on said driven shaft for selectively permitting manual rotation of the driven shaft and first-named shaft for adjustment of the position of the frame member along the vertical axis. 